1. Field of the Invention
The invention relates in general to a redistribution layer structure of a wafer and the fabricating method thereof, and more particularly to a redistribution layer having two different metallic layers.
2. Description of the Related Art
Referring to FIG. 1, a cross-sectional view of a traditional wafer. The traditional wafer 10 includes a wafer 11, a conductor 14, a first passivation layer 13, a redistribution layer 14, a second passivation layer 15, a under bump metallurgy layer (UBM layer) 16, and a bump 17. The conductor, such as a pad 12, is disposed on the wafer 11. The first passivation layer 13 covers the wafer 11 and part of the pad 12, and exposes the surface of the pad 12. The redistribution layer 14 is formed on the first passivation layer 13 for electrically connecting to the pad 12 and UBM layer 16. The redistribution layer 14 is generally made from aluminum. The second passivation layer 15 is disposed on the redistribution layer 14 for protecting it. The UBM layer 16 is formed on one end of the redistribution layer 14 for helping connect the bump 17 to the redistribution layer 14. The bump 17 is formed on the UBM layer 16.
Referring to FIG. 2A˜2H, cross sectional views showing a method for fabricating the traditional redistribution layer of a wafer. The method for fabricating the traditional redistribution layer includes several steps stated below. First, a wafer 11 having a pad 12 is provided as shown FIG. 2A. Then, a first passivation layer 13 is coated on the wafer 11 and part of the pad 12 as shown in FIG. 2B. The first passivation layer 13 exposes the surface 121 of the pad 12. Next, a patterned conductive layer 14a is formed on the first passivation layer 13 and the pad 12 as shown FIG. 2C. Then, a second passivation layer 15 is coated on the redistribution layer 14. An aperture 151 of the second passivation layer 15 is formed and exposes part of the redistribution layer 14 as shown in FIG. 2D. Afterward, a UBM layer 16 is formed in the aperture 151.
Next, a photoresist layer 181 covers the whole surface, and then a opening 182 is defined by patterning as shown in FIG. 2F. Then, the solder paste 19 is printed into the opening 182 as shown in FIG. 2G. Finally, the solder paste 19 is reflowed to forming the bump 17, and the patterned photoresist layer is removed. Thus, the wafer 10 is made.
However, the redistribution layer is easily detached from the passivation layer of the traditional wafer. It is difficult for the redistribution layer to tightly fasten on the first passivation layer, and that results in the failure of the wafer.